Slot antennas and arrays thereof are widely used for transmission of electromagnetic signals. An example of such antennas is disclosed in applicant's U.S. Pat. No. 3,587,108, issued June 22, l971.
Antennas employed for the transmission of television signals are required to transmit signals covering at least six megaHertz, and often a several times greater bandwidth if, e.g., the antenna is used for several channels.
In the design of slot antennas it is often desirable to have large impedance bandwidth (i.e. low Q), and also to have omnidirectional radiation patterns in the plane transverse to the slot (E plane). To a first order the impedance bandwidth of a slot is a direct function of slot volume. However, the departure of E plane pattern from omnidirectional, and the difficulty of arraying efficiently, are both inverse functions of slot volume; i.e. the slot should be short and small in cross section (girth) to meet these latter requirements. Therefore, slot design often requires considerable compromise if e.g. E plane pattern variation of less than .+-. 3 db (considered omnidirectional in the industry), VSWR under 1.1 over 20% or more bands, and linear arraying of many slots are required simultaneously. Mechanically, it is also desirable to combine an array of slot antennas into a long linear array of slots using a single continuous cavity.
It has been found that by use of a particular size slot exciting strap, located in the cavity and fed in a manner described more fully hereinafter, it is possible to obtain low Q, a small cavity length and cross section while achieving the pattern, VSWR, and arraying properties required.
The above description, as well as further objects, features and advantages of the present invention, will be more fully appreciated by reference to the following detailed description of a presently preferred, but nonetheless illustrative, embodiment in accordance with the present invention when taken in conjunction with the accompanying drawings.